There is a demand in vehicles with internal combustion engines for supplemental heat during the warm-up phase that immediately follows a cold-start in cold ambient (winter) conditions. This is particularly true in vehicles with diesel engines since they warm up more slowly than spark-ignition engines. One of the main benefits of rapid warm-up of an engine is improved heater and defroster performance. Also, warm engines run more efficiently and produce lower emissions levels than cold engines.
Additionally, diesel engines have the additional challenge of providing sufficient heat when the vehicle is stuck in a traffic jam in cold ambient conditions. Under some conditions, the engine may not naturally reject sufficient heat to the cooling system to maintain the engine to its set-point. In these cases, supplemental heat may be required long after the cold-start event.
The currently known methods of generating supplemental heat include: (1) electric resistance heating; (2) extra fuel burner and heat exchanger; (3) exhaust system heat exchanger; and (4) viscous heater driven by the engine.
It is known that a direct driven coolant circulation pump in an engine delivers more coolant flow to the engine than is needed at part-throttle or part-load, since the pump is sized for full-throttle or full load at all engine speeds. Since the extra pumping work represents parasitic loss, various systems have been devised to match coolant pump speed to the instantaneous power level rather than just engine speed. Known methods to provide continuously-variable coolant pump speed are: (1) electric motor driven coolant pumps; (2) variable mechanical drives; and (3) variable viscous drives.
Thus, a need exists for improved supplemental heat sources and systems for vehicle engines, particularly for the warmup phases and for diesel engines. Also, a need exists for a variable coolant pump, especially for use in producing supplemental heat for a vehicle.